Performance of Pinus contorta inoculated with two strains of root endophytic fungus, Phialocephala fortinii: effects of synthesis system and glucose concentration

Melanized, root-colonizing fungi are ubiquitous. Their ecological role, how ever, is poorly understood, and results of studies of associations between these fungi and their potential host plants are controversial. The culture system under which the association is studied may also affect the host-fung us interaction. Two experiments on the association between Pinus contorta D ougl. ex Loud., and a root-inhabiting endophytic fungus, Phialocephala fort inii Wang & Wilcox, were conducted to study the host response to inoculatio n. First, Pinus contorta seedlings were inoculated with two strains of Phia locephala fortinii and grown under aseptic conditions with five levels of g lucose in the medium. Multiple linear regression analysis was employed to s tudy the effects of inoculation and glucose concentration. Second, the same two strains of Phialocephala fortinii were inoculated on Pinus contorta se edlings in open pot cultures. Inoculation resulted in substantial increase in all biomass components of the host plant in the aseptic culture system. Total biomass, for example, was increased approximately 60 and 90% when see dlings were inoculated with strain 1 and strain 2, respectively. No seedlin g mortality was observed following fungal inoculation after 6 months of inc ubation. Inoculation increased host biomass with increasing glucose concent ration, while glucose concentration did not significantly affect host bioma ss when no inoculum was added. Inoculation lowered foliar nitrogen and phos phorus concentrations. The effect of glucose concentration on the foliar nu trient concentrations varied between the two strains. In the open pot cultu res, inoculation did not affect biomass or foliar nutrient concentration. W e hypothesise that the observed increases in host growth in the aseptic cul ture system are due to fungal respiration in a closed culture system, the c arbohydrates made available to the host plant by the fungus, or, most likel y, to a combination of both factors. The ecological role of Phialocephala f ortinii and the validity of aseptic culture assays are discussed.